feat: schema snapshot models + PG/MySQL/SQLite capture with 5k cap (Task 12)

desktop/src-tauri/src/db/introspection.rs

@@ -912,3 +912,98 @@ pub fn pg_hypertables_query(_schema: &str) -> String {
      ORDER BY h.hypertable_name"
         .to_string()
 }
+
+// ---------------------------------------------------------------------------
+// Schema-diff snapshot queries (0.8.0) — one set-based query per object class
+// ---------------------------------------------------------------------------
+
+/// Table columns with resolved types, nullability, and defaults.
+/// Columns: table_name, column_name, data_type, is_nullable, default_expr
+pub fn pg_diff_columns_query() -> String {
+    "SELECT c.relname, a.attname, \
+     pg_catalog.format_type(a.atttypid, a.atttypmod), \
+     NOT a.attnotnull, \
+     pg_catalog.pg_get_expr(d.adbin, d.adrelid) \
+     FROM pg_catalog.pg_class c \
+     JOIN pg_catalog.pg_namespace n ON n.oid = c.relnamespace \
+     JOIN pg_catalog.pg_attribute a ON a.attrelid = c.oid AND a.attnum > 0 AND NOT a.attisdropped \
+     LEFT JOIN pg_catalog.pg_attrdef d ON d.adrelid = c.oid AND d.adnum = a.attnum \
+     WHERE n.nspname = $1 AND c.relkind IN ('r', 'p') \
+     ORDER BY c.relname, a.attnum"
+        .to_string()
+}
+
+/// Constraints (PK/UNIQUE/CHECK/FK) with exact column lists and FK metadata.
+/// Columns: table_name, constraint_name, contype, cols, ref_cols, ref_table, confdeltype, confupdtype, definition
+pub fn pg_diff_constraints_query() -> String {
+    "SELECT cl.relname, con.conname, con.contype::text, \
+     (SELECT string_agg(a.attname, ', ' ORDER BY k.ord) \
+        FROM unnest(con.conkey) WITH ORDINALITY AS k(attnum, ord) \
+        JOIN pg_attribute a ON a.attrelid = con.conrelid AND a.attnum = k.attnum), \
+     (SELECT string_agg(a.attname, ', ' ORDER BY k.ord) \
+        FROM unnest(con.confkey) WITH ORDINALITY AS k(attnum, ord) \
+        JOIN pg_attribute a ON a.attrelid = con.confrelid AND a.attnum = k.attnum), \
+     (SELECT n2.nspname || '.' || cl2.relname \
+        FROM pg_class cl2 JOIN pg_namespace n2 ON n2.oid = cl2.relnamespace \
+        WHERE cl2.oid = con.confrelid), \
+     con.confdeltype::text, con.confupdtype::text, \
+     pg_get_constraintdef(con.oid, true) \
+     FROM pg_catalog.pg_constraint con \
+     JOIN pg_catalog.pg_class cl ON cl.oid = con.conrelid \
+     JOIN pg_catalog.pg_namespace n ON n.oid = cl.relnamespace \
+     WHERE n.nspname = $1 AND con.contype IN ('p', 'u', 'c', 'f') \
+     ORDER BY cl.relname, con.contype, con.conname"
+        .to_string()
+}
+
+/// Secondary indexes (constraint-backed indexes excluded), with column lists.
+/// Columns: table_name, index_name, is_unique, cols
+pub fn pg_diff_indexes_query() -> String {
+    "SELECT t.relname, i.relname, ix.indisunique, \
+     (SELECT string_agg(a.attname, ', ' ORDER BY k.ord) \
+        FROM unnest(ix.indkey) WITH ORDINALITY AS k(attnum, ord) \
+        JOIN pg_attribute a ON a.attrelid = ix.indrelid AND a.attnum = k.attnum \
+        WHERE k.attnum > 0) \
+     FROM pg_index ix \
+     JOIN pg_class i ON i.oid = ix.indexrelid \
+     JOIN pg_class t ON t.oid = ix.indrelid \
+     JOIN pg_namespace n ON n.oid = t.relnamespace \
+     WHERE n.nspname = $1 AND NOT ix.indisprimary \
+       AND NOT EXISTS (SELECT 1 FROM pg_constraint con WHERE con.conindid = i.oid) \
+     ORDER BY t.relname, i.relname"
+        .to_string()
+}
+
+/// Views + materialized views. Columns: schema, name, definition, materialized
+pub fn pg_diff_views_query() -> String {
+    "SELECT v.schemaname, v.viewname, v.definition, false \
+     FROM pg_views v WHERE v.schemaname = $1 \
+     UNION ALL \
+     SELECT v.schemaname, v.matviewname, v.definition, true \
+     FROM pg_matviews v WHERE v.schemaname = $1 \
+     ORDER BY 2"
+        .to_string()
+}
+
+/// Sequences. Columns: schema, name, start, increment, min, max, cycle
+pub fn pg_diff_sequences_query() -> String {
+    "SELECT sequence_schema, sequence_name, \
+     COALESCE(start_value::text, '1'), COALESCE(increment::text, '1'), \
+     COALESCE(minimum_value::text, '1'), COALESCE(maximum_value::text, '9223372036854775807'), \
+     cycle_option = 'YES' \
+     FROM information_schema.sequences \
+     WHERE sequence_schema = $1 \
+     ORDER BY sequence_name"
+        .to_string()
+}
+
+/// Enums with ordered labels. Columns: schema, name, label (row per label)
+pub fn pg_diff_enums_query() -> String {
+    "SELECT n.nspname, t.typname, e.enumlabel \
+     FROM pg_type t \
+     JOIN pg_namespace n ON n.oid = t.typnamespace \
+     JOIN pg_enum e ON e.enumtypid = t.oid \
+     WHERE t.typtype = 'e' AND n.nspname = $1 \
+     ORDER BY t.typname, e.enumsortorder"
+        .to_string()
+}

desktop/src-tauri/src/db/mod.rs

@@ -5,6 +5,7 @@ pub mod object_crud;
 pub mod object_ddl;
 pub mod pool;
 pub mod tls;
+pub mod schema_diff;
 
 #[allow(unused_imports)]
 pub use pool::{ConnectionPoolManager, DbConfig, DbHandle};

desktop/src-tauri/src/db/mysql.rs

@@ -323,4 +323,64 @@ mod tests {
         assert_eq!(mysql_default_sort(&["name".into()]), "name");
         assert_eq!(mysql_default_sort(&[]), "");
     }
-}
+}
+// ── Schema-diff snapshot queries (0.8.0) ──────────────────────────────
+
+/// Columns: table_name, column_name, column_type, is_nullable, column_default
+pub fn mysql_snapshot_columns_query(schema: &str) -> String {
+    format!(
+        "SELECT table_name, column_name, column_type, is_nullable, \
+         COALESCE(column_default, '') \
+         FROM information_schema.columns \
+         WHERE table_schema = '{}' \
+         ORDER BY table_name, ordinal_position",
+        schema.replace('\'', "''")
+    )
+}
+
+/// Constraints (one row per constraint-column). Columns: table_name,
+/// constraint_name, constraint_type, column_name, referenced_table_name,
+/// delete_rule, update_rule, check_clause
+pub fn mysql_snapshot_constraints_query(schema: &str) -> String {
+    format!(
+        "SELECT kcu.table_name, kcu.constraint_name, tc.constraint_type, kcu.column_name, \
+         COALESCE(kcu.referenced_table_name, ''), \
+         COALESCE(rc.delete_rule, ''), COALESCE(rc.update_rule, ''), \
+         COALESCE((SELECT cc.check_clause FROM information_schema.check_constraints cc \
+            WHERE cc.constraint_schema = kcu.constraint_schema \
+              AND cc.constraint_name = kcu.constraint_name), '') \
+         FROM information_schema.key_column_usage kcu \
+         LEFT JOIN information_schema.table_constraints tc \
+           ON tc.constraint_schema = kcu.constraint_schema \
+          AND tc.constraint_name = kcu.constraint_name \
+          AND tc.table_name = kcu.table_name \
+         LEFT JOIN information_schema.referential_constraints rc \
+           ON rc.constraint_schema = kcu.constraint_schema \
+          AND rc.constraint_name = kcu.constraint_name \
+         WHERE kcu.constraint_schema = '{}' AND tc.constraint_type IS NOT NULL \
+         ORDER BY kcu.table_name, kcu.constraint_name, kcu.ordinal_position",
+        schema.replace('\'', "''")
+    )
+}
+
+/// Secondary indexes (one row per index-column). Columns: table_name,
+/// index_name, non_unique, column_name
+pub fn mysql_snapshot_indexes_query(schema: &str) -> String {
+    format!(
+        "SELECT table_name, index_name, non_unique, column_name \
+         FROM information_schema.statistics \
+         WHERE table_schema = '{}' AND index_name != 'PRIMARY' \
+         ORDER BY table_name, index_name, seq_in_index",
+        schema.replace('\'', "''")
+    )
+}
+
+/// Views. Columns: table_schema, table_name, view_definition
+pub fn mysql_snapshot_views_query(schema: &str) -> String {
+    format!(
+        "SELECT table_schema, table_name, view_definition \
+         FROM information_schema.views \
+         WHERE table_schema = '{}'",
+        schema.replace('\'', "''")
+    )
+}

desktop/src-tauri/src/db/schema_diff.rs

@@ -0,0 +1,508 @@
+//! Schema snapshot capture + the pure diff engine (engine lands in Task 14).
+//!
+//! Snapshots are read-only, single-use, and capped (5,000 objects — spec §2).
+//! Sync SQL is generated in the TARGET's dialect with identifiers quoted
+//! per engine (spec §2: never raw interpolation).
+
+use crate::db::pool::DbHandle;
+use crate::models::db_viewer::*;
+use std::collections::BTreeMap;
+
+pub(crate) const SNAPSHOT_CAP: usize = 5_000;
+
+/// Map a PG `conf*type` action code to its SQL name.
+pub(crate) fn pg_fk_action(code: &str) -> &'static str {
+    match code {
+        "r" => "RESTRICT",
+        "c" => "CASCADE",
+        "n" => "SET NULL",
+        "d" => "SET DEFAULT",
+        _ => "NO ACTION",
+    }
+}
+
+/// Enforce the 5,000-object cap, setting `truncated` (never silent).
+pub(crate) fn apply_snapshot_cap(snap: &mut SchemaSnapshot) {
+    let mut total = snap.tables.len() + snap.views.len() + snap.sequences.len() + snap.enums.len();
+    let over = total > SNAPSHOT_CAP;
+    if over {
+        let mut remaining = SNAPSHOT_CAP;
+        fn take<T>(v: &mut Vec<T>, budget: &mut usize) {
+            if v.len() > *budget {
+                v.truncate(*budget);
+            }
+            *budget -= v.len();
+        }
+        take(&mut snap.tables, &mut remaining);
+        take(&mut snap.views, &mut remaining);
+        take(&mut snap.sequences, &mut remaining);
+        take(&mut snap.enums, &mut remaining);
+        total = SNAPSHOT_CAP;
+    }
+    snap.object_count = total;
+    snap.truncated = over;
+}
+
+fn csv_names(s: &str) -> Vec<String> {
+    s.split(", ").map(|p| p.trim().to_string()).filter(|p| !p.is_empty()).collect()
+}
+
+/// Capture a PostgreSQL schema snapshot (six set-based queries, one per class).
+pub(crate) async fn capture_pg(
+    client: &tokio_postgres::Client,
+    engine: &str,
+    schema: &str,
+) -> Result<SchemaSnapshot, String> {
+    let mut tables: BTreeMap<String, SnapshotTable> = BTreeMap::new();
+    let mut views: Vec<SnapshotView> = Vec::new();
+    let mut sequences: Vec<SnapshotSequence> = Vec::new();
+    let mut enums: BTreeMap<String, SnapshotEnum> = BTreeMap::new();
+
+    // Columns
+    let rows = client
+        .query(&crate::db::introspection::pg_diff_columns_query(), &[&schema])
+        .await
+        .map_err(|e| format!("columns query failed: {e}"))?;
+    for r in rows {
+        let tname: String = r.get(0);
+        let entry = tables.entry(tname.clone()).or_insert_with(|| SnapshotTable {
+            schema: schema.to_string(),
+            name: tname,
+            ..Default::default()
+        });
+        entry.columns.push(SnapshotColumn {
+            name: r.get(1),
+            data_type: r.get(2),
+            nullable: r.get(3),
+            default_value: r.get::<_, Option<String>>(4),
+        });
+    }
+
+    // Constraints (PK / UNIQUE / CHECK / FK)
+    // Column order: table_name(0), constraint_name(1), contype(2), cols(3),
+    // ref_cols(4), ref_table(5), confdeltype(6), confupdtype(7), definition(8)
+    let rows = client
+        .query(&crate::db::introspection::pg_diff_constraints_query(), &[&schema])
+        .await
+        .map_err(|e| format!("constraints query failed: {e}"))?;
+    for r in rows {
+        let tname: String = r.get(0);
+        let cname: String = r.get(1);
+        let contype: String = r.get(2);
+        let Some(entry) = tables.get_mut(&tname) else { continue };
+        match contype.as_str() {
+            "p" => entry.primary_key = csv_names(&r.get::<_, Option<String>>(3).unwrap_or_default()),
+            "u" => entry.uniques.push(SnapshotConstraint {
+                name: cname,
+                kind: "unique".into(),
+                definition: r.get::<_, Option<String>>(3).unwrap_or_default(),
+            }),
+            "c" => entry.checks.push(SnapshotConstraint {
+                name: cname,
+                kind: "check".into(),
+                definition: r.get::<_, Option<String>>(8).unwrap_or_default(),
+            }),
+            "f" => {
+                let ref_qualified: Option<String> = r.get(5);
+                let (ref_schema, ref_table) = ref_qualified
+                    .map(|q| match q.split_once('.') {
+                        Some((s, t)) => (s.to_string(), t.to_string()),
+                        None => (String::new(), q.clone()),
+                    })
+                    .unwrap_or_default();
+                entry.foreign_keys.push(SnapshotFk {
+                    name: cname,
+                    columns: csv_names(&r.get::<_, Option<String>>(3).unwrap_or_default()),
+                    ref_schema,
+                    ref_table,
+                    ref_columns: csv_names(&r.get::<_, Option<String>>(4).unwrap_or_default()),
+                    on_delete: pg_fk_action(&r.get::<_, Option<String>>(6).unwrap_or_default()).to_string(),
+                    on_update: pg_fk_action(&r.get::<_, Option<String>>(7).unwrap_or_default()).to_string(),
+                });
+            }
+            _ => {}
+        }
+    }
+
+    // Indexes
+    let rows = client
+        .query(&crate::db::introspection::pg_diff_indexes_query(), &[&schema])
+        .await
+        .map_err(|e| format!("indexes query failed: {e}"))?;
+    for r in rows {
+        let tname: String = r.get(0);
+        let Some(entry) = tables.get_mut(&tname) else { continue };
+        entry.indexes.push(SnapshotIndex {
+            name: r.get(1),
+            columns: csv_names(&r.get::<_, Option<String>>(3).unwrap_or_default()),
+            unique: r.get(2),
+        });
+    }
+
+    // Views + matviews
+    let rows = client
+        .query(&crate::db::introspection::pg_diff_views_query(), &[&schema])
+        .await
+        .map_err(|e| format!("views query failed: {e}"))?;
+    for r in rows {
+        views.push(SnapshotView {
+            schema: r.get(0),
+            name: r.get(1),
+            definition: r.get(2),
+            materialized: r.get(3),
+        });
+    }
+
+    // Sequences
+    let rows = client
+        .query(&crate::db::introspection::pg_diff_sequences_query(), &[&schema])
+        .await
+        .map_err(|e| format!("sequences query failed: {e}"))?;
+    for r in rows {
+        sequences.push(SnapshotSequence {
+            schema: r.get(0),
+            name: r.get(1),
+            start: r.get(2),
+            increment: r.get(3),
+            minimum: r.get(4),
+            maximum: r.get(5),
+            cycle: r.get(6),
+        });
+    }
+
+    // Enums (one row per label — aggregate by name)
+    let rows = client
+        .query(&crate::db::introspection::pg_diff_enums_query(), &[&schema])
+        .await
+        .map_err(|e| format!("enums query failed: {e}"))?;
+    for r in rows {
+        let ename: String = r.get(1);
+        let entry = enums.entry(ename.clone()).or_insert_with(|| SnapshotEnum {
+            schema: r.get(0),
+            name: ename,
+            labels: Vec::new(),
+        });
+        entry.labels.push(r.get(2));
+    }
+
+    let mut snap = SchemaSnapshot {
+        engine: engine.to_string(),
+        schema: schema.to_string(),
+        tables: tables.into_values().collect(),
+        views,
+        sequences,
+        enums: enums.into_values().collect(),
+        object_count: 0,
+        truncated: false,
+    };
+    apply_snapshot_cap(&mut snap);
+    Ok(snap)
+}
+
+/// Capture a SQLite (in-file/in-memory) snapshot.
+pub(crate) fn capture_sqlite(conn: &rusqlite::Connection) -> Result<SchemaSnapshot, String> {
+    crate::db::schema_diff::capture::sqlite(conn)
+}
+
+/// Capture a MySQL/MariaDB snapshot.
+pub(crate) async fn capture_mysql(
+    conn: &mut sqlx::mysql::MySqlConnection,
+    engine: &str,
+    schema: &str,
+) -> Result<SchemaSnapshot, String> {
+    crate::db::schema_diff::capture::mysql(conn, engine, schema).await
+}
+
+/// Dispatch a snapshot capture across engines. `engine` is the CONNECTION's
+/// db_type (mariadb vs mysql matters for the diff dialect).
+pub(crate) async fn capture_snapshot(
+    handle: &DbHandle,
+    engine: &str,
+    schema: &str,
+) -> Result<SchemaSnapshot, String> {
+    match handle {
+        DbHandle::Postgresql(client, _) => capture_pg(client, engine, schema).await,
+        DbHandle::MySql(pool) => {
+            let mut conn = pool
+                .acquire()
+                .await
+                .map_err(|e| format!("source/target connection failed: {e}"))?;
+            capture_mysql(&mut *conn, engine, schema).await
+        }
+        DbHandle::Sqlite(conn) => capture_sqlite(conn),
+    }
+}
+
+pub(crate) mod capture {
+    use super::*;
+
+    pub(crate) fn sqlite(conn: &rusqlite::Connection) -> Result<SchemaSnapshot, String> {
+        let mut snap = SchemaSnapshot {
+            engine: "sqlite".into(),
+            schema: "main".into(),
+            ..Default::default()
+        };
+
+        let mut stmt = conn
+            .prepare("SELECT type, name, sql FROM sqlite_master WHERE name NOT LIKE 'sqlite_%' AND type IN ('table', 'view') ORDER BY name")
+            .map_err(|e| e.to_string())?;
+        let objects: Vec<(String, String, Option<String>)> = stmt
+            .query_map([], |r| Ok((r.get(0)?, r.get(1)?, r.get(2)?)))
+            .map_err(|e| e.to_string())?
+            .filter_map(|r| r.ok())
+            .collect();
+
+        for (otype, name, sql) in objects {
+            if otype == "view" {
+                snap.views.push(SnapshotView {
+                    schema: "main".into(),
+                    name,
+                    definition: sql.unwrap_or_default(),
+                    materialized: false,
+                });
+                continue;
+            }
+            let mut table = SnapshotTable {
+                schema: "main".into(),
+                name: name.clone(),
+                ..Default::default()
+            };
+            // Columns + PK + defaults
+            let mut cols = conn
+                .prepare(&format!("PRAGMA table_info({})", quote_double(&name)))
+                .map_err(|e| e.to_string())?;
+            let col_rows: Vec<(String, String, i64, Option<String>, i64)> = cols
+                .query_map([], |r| Ok((r.get(1)?, r.get(2)?, r.get(3)?, r.get(4)?, r.get(5)?)))
+                .map_err(|e| e.to_string())?
+                .filter_map(|r| r.ok())
+                .collect();
+            drop(cols);
+            for (cname, ctype, notnull, default, pk) in col_rows {
+                if pk > 0 {
+                    table.primary_key.push(cname.clone());
+                }
+                table.columns.push(SnapshotColumn {
+                    name: cname,
+                    data_type: ctype,
+                    nullable: notnull == 0,
+                    default_value: default,
+                });
+            }
+            // Indexes (skip the PK-mandated sqlite_autoindex_*)
+            let mut idx = conn
+                .prepare(&format!("PRAGMA index_list({})", quote_double(&name)))
+                .map_err(|e| e.to_string())?;
+            let idx_rows: Vec<(String, i64)> = idx
+                .query_map([], |r| Ok((r.get(1)?, r.get(2)?)))
+                .map_err(|e| e.to_string())?
+                .filter_map(|r| r.ok())
+                .collect();
+            drop(idx);
+            for (iname, unique) in idx_rows {
+                if iname.starts_with("sqlite_autoindex") {
+                    continue;
+                }
+                let mut info = conn
+                    .prepare(&format!("PRAGMA index_info({})", quote_double(&iname)))
+                    .map_err(|e| e.to_string())?;
+                let icols: Vec<String> = info
+                    .query_map([], |r| r.get::<_, String>(2))
+                    .map_err(|e| e.to_string())?
+                    .filter_map(|r| r.ok())
+                    .collect();
+                drop(info);
+                table.indexes.push(SnapshotIndex {
+                    name: iname,
+                    columns: icols,
+                    unique: unique != 0,
+                });
+            }
+            // Foreign keys
+            let mut fks = conn
+                .prepare(&format!("PRAGMA foreign_key_list({})", quote_double(&name)))
+                .map_err(|e| e.to_string())?;
+            let fk_rows: Vec<(i64, i64, String, String, String, String, String)> = fks
+                .query_map([], |r| {
+                    Ok((r.get(0)?, r.get(1)?, r.get(2)?, r.get(3)?, r.get(4)?, r.get(5)?, r.get(6)?))
+                })
+                .map_err(|e| e.to_string())?
+                .filter_map(|r| r.ok())
+                .collect();
+            drop(fks);
+            // (id, seq, table, from, to, on_update, on_delete) — group by id
+            let mut grouped: BTreeMap<i64, SnapshotFk> = BTreeMap::new();
+            for (id, _seq, reftable, from, to, on_update, on_delete) in fk_rows {
+                let fk = grouped.entry(id).or_insert_with(|| SnapshotFk {
+                    name: format!("fk_{name}_{id}"),
+                    columns: Vec::new(),
+                    ref_schema: "main".into(),
+                    ref_table: reftable,
+                    ref_columns: Vec::new(),
+                    on_delete: String::new(),
+                    on_update: String::new(),
+                });
+                fk.columns.push(from);
+                if !to.is_empty() {
+                    fk.ref_columns.push(to);
+                }
+                if !on_delete.is_empty() {
+                    fk.on_delete = on_delete.to_uppercase();
+                }
+                if !on_update.is_empty() {
+                    fk.on_update = on_update.to_uppercase();
+                }
+            }
+            table.foreign_keys = grouped.into_values().collect();
+            snap.tables.push(table);
+        }
+
+        apply_snapshot_cap(&mut snap);
+        Ok(snap)
+    }
+
+    pub(crate) async fn mysql(
+        conn: &mut sqlx::mysql::MySqlConnection,
+        engine: &str,
+        schema: &str,
+    ) -> Result<SchemaSnapshot, String> {
+        use crate::db::mysql::{mysql_row_string, mysql_snapshot_columns_query, mysql_snapshot_constraints_query, mysql_snapshot_indexes_query, mysql_snapshot_views_query};
+
+        let mut tables: BTreeMap<String, SnapshotTable> = BTreeMap::new();
+        let mut views: Vec<SnapshotView> = Vec::new();
+
+        let rows = sqlx::query(&mysql_snapshot_columns_query(schema))
+            .fetch_all(&mut *conn)
+            .await
+            .map_err(|e| format!("columns query failed: {e}"))?;
+        for r in rows {
+            let tname = mysql_row_string(&r, 0);
+            let entry = tables.entry(tname.clone()).or_insert_with(|| SnapshotTable {
+                schema: schema.to_string(),
+                name: tname,
+                ..Default::default()
+            });
+            entry.columns.push(SnapshotColumn {
+                name: mysql_row_string(&r, 1),
+                data_type: mysql_row_string(&r, 2),
+                nullable: mysql_row_string(&r, 3) == "YES",
+                default_value: (!mysql_row_string(&r, 4).is_empty()).then(|| mysql_row_string(&r, 4)),
+            });
+        }
+
+        let rows = sqlx::query(&mysql_snapshot_constraints_query(schema))
+            .fetch_all(&mut *conn)
+            .await
+            .map_err(|e| format!("constraints query failed: {e}"))?;
+        for r in rows {
+            let tname = mysql_row_string(&r, 0);
+            let cname = mysql_row_string(&r, 1);
+            let ctype = mysql_row_string(&r, 2);
+            let col = mysql_row_string(&r, 3);
+            let Some(entry) = tables.get_mut(&tname) else { continue };
+            match ctype.as_str() {
+                "PRIMARY KEY" => {
+                    if !entry.primary_key.contains(&col) {
+                        entry.primary_key.push(col);
+                    }
+                }
+                "UNIQUE" => {
+                    if let Some(u) = entry.uniques.iter_mut().find(|u| u.name == cname) {
+                        u.definition = if u.definition.is_empty() { col.clone() } else { format!("{}, {col}", u.definition) };
+                    } else {
+                        entry.uniques.push(SnapshotConstraint {
+                            name: cname,
+                            kind: "unique".into(),
+                            definition: col,
+                        });
+                    }
+                }
+                "FOREIGN KEY" => {
+                    let ref_table = mysql_row_string(&r, 4);
+                    let on_delete = mysql_row_string(&r, 5).to_uppercase();
+                    let on_update = mysql_row_string(&r, 6).to_uppercase();
+                    if let Some(fk) = entry.foreign_keys.iter_mut().find(|f| f.name == cname) {
+                        fk.columns.push(col);
+                    } else {
+                        entry.foreign_keys.push(SnapshotFk {
+                            name: cname,
+                            columns: vec![col],
+                            ref_schema: String::new(),
+                            ref_table,
+                            ref_columns: Vec::new(),
+                            on_delete,
+                            on_update,
+                        });
+                    }
+                }
+                "CHECK" => {
+                    if let Some(c) = entry.checks.iter_mut().find(|c| c.name == cname) {
+                        c.definition = format!("{} {}", c.definition, mysql_row_string(&r, 7));
+                    } else {
+                        entry.checks.push(SnapshotConstraint {
+                            name: cname,
+                            kind: "check".into(),
+                            definition: mysql_row_string(&r, 7),
+                        });
+                    }
+                }
+                _ => {}
+            }
+        }
+
+        let rows = sqlx::query(&mysql_snapshot_indexes_query(schema))
+            .fetch_all(&mut *conn)
+            .await
+            .map_err(|e| format!("indexes query failed: {e}"))?;
+        for r in rows {
+            let tname = mysql_row_string(&r, 0);
+            let iname = mysql_row_string(&r, 1);
+            let unique = mysql_row_string(&r, 2) == "0";
+            let col = mysql_row_string(&r, 3);
+            let Some(entry) = tables.get_mut(&tname) else { continue };
+            if let Some(ix) = entry.indexes.iter_mut().find(|i| i.name == iname) {
+                ix.columns.push(col);
+            } else {
+                entry.indexes.push(SnapshotIndex {
+                    name: iname,
+                    columns: vec![col],
+                    unique,
+                });
+            }
+        }
+
+        let rows = sqlx::query(&mysql_snapshot_views_query(schema))
+            .fetch_all(&mut *conn)
+            .await
+            .map_err(|e| format!("views query failed: {e}"))?;
+        for r in rows {
+            views.push(SnapshotView {
+                schema: mysql_row_string(&r, 0),
+                name: mysql_row_string(&r, 1),
+                definition: mysql_row_string(&r, 2),
+                materialized: false,
+            });
+        }
+
+        let mut snap = SchemaSnapshot {
+            engine: engine.to_string(),
+            schema: schema.to_string(),
+            tables: tables.into_values().collect(),
+            views,
+            sequences: Vec::new(),
+            enums: Vec::new(),
+            object_count: 0,
+            truncated: false,
+        };
+        apply_snapshot_cap(&mut snap);
+        Ok(snap)
+    }
+}
+
+/// Double-quote an identifier (PG/SQLite) with embedded-quote doubling.
+pub(crate) fn quote_double(name: &str) -> String {
+    format!("\"{}\"", name.replace('"', "\"\""))
+}
+
+#[cfg(test)]
+#[path = "schema_diff.test.rs"]
+mod schema_diff_tests;

desktop/src-tauri/src/db/schema_diff.test.rs

@@ -0,0 +1,159 @@
+use super::*;
+
+// ── Pure helpers (PG constraint row mapping) ────────────────────────
+
+#[test]
+fn pg_fk_action_maps_codes() {
+    assert_eq!(pg_fk_action("a"), "NO ACTION");
+    assert_eq!(pg_fk_action("r"), "RESTRICT");
+    assert_eq!(pg_fk_action("c"), "CASCADE");
+    assert_eq!(pg_fk_action("n"), "SET NULL");
+    assert_eq!(pg_fk_action("d"), "SET DEFAULT");
+    assert_eq!(pg_fk_action("x"), "NO ACTION");
+}
+
+#[test]
+fn snapshot_cap_sets_truncated() {
+    // 5,001 objects → truncated report, never silent (spec §2)
+    let mut snap = SchemaSnapshot::default();
+    snap.engine = "postgresql".into();
+    snap.schema = "s".into();
+    for i in 0..5_001 {
+        snap.tables.push(SnapshotTable {
+            schema: "s".into(),
+            name: format!("t{i}"),
+            columns: vec![],
+            primary_key: vec![],
+            uniques: vec![],
+            checks: vec![],
+            indexes: vec![],
+            foreign_keys: vec![],
+        });
+    }
+    apply_snapshot_cap(&mut snap);
+    assert!(snap.truncated);
+    assert!(snap.object_count <= 5_000);
+    assert_eq!(snap.tables.len(), snap.object_count);
+}
+
+#[test]
+fn query_builders_target_the_right_catalogs() {
+    let cols = crate::db::introspection::pg_diff_columns_query();
+    assert!(cols.contains("pg_attribute") && cols.contains("format_type"));
+    let cons = crate::db::introspection::pg_diff_constraints_query();
+    assert!(cons.contains("pg_constraint") && cons.contains("contype"));
+    let idx = crate::db::introspection::pg_diff_indexes_query();
+    assert!(idx.contains("pg_index") && idx.contains("indisunique"));
+    let views = crate::db::introspection::pg_diff_views_query();
+    assert!(views.contains("pg_views") && views.contains("pg_matviews"));
+    let seqs = crate::db::introspection::pg_diff_sequences_query();
+    assert!(seqs.contains("information_schema.sequences"));
+    let enums = crate::db::introspection::pg_diff_enums_query();
+    assert!(enums.contains("pg_type") && enums.contains("pg_enum"));
+}
+
+// ── SQLite capture (in-memory, real, NOT ignored) ──────────────────
+
+#[test]
+fn sqlite_capture_reads_pragmas() {
+    let conn = rusqlite::Connection::open_in_memory().unwrap();
+    conn.execute_batch(
+        "CREATE TABLE users (id INTEGER PRIMARY KEY, name TEXT NOT NULL DEFAULT 'x', email TEXT);
+         CREATE UNIQUE INDEX idx_users_email ON users(email);
+         CREATE TABLE orders (id INTEGER PRIMARY KEY, user_id INTEGER REFERENCES users(id) ON DELETE CASCADE);
+         CREATE VIEW v_users AS SELECT id, name FROM users;",
+    )
+    .unwrap();
+    let snap = capture_sqlite(&conn).expect("capture");
+    assert_eq!(snap.engine, "sqlite");
+    assert_eq!(snap.tables.len(), 2);
+    let users = snap.tables.iter().find(|t| t.name == "users").unwrap();
+    assert_eq!(users.primary_key, vec!["id"]);
+    assert_eq!(users.columns.len(), 3);
+    assert!(users.columns.iter().any(|c| c.name == "name" && !c.nullable));
+    assert!(users.columns.iter().any(|c| c.name == "email" && c.nullable));
+    assert!(users.indexes.iter().any(|i| i.name == "idx_users_email" && i.unique));
+    let orders = snap.tables.iter().find(|t| t.name == "orders").unwrap();
+    assert_eq!(orders.foreign_keys.len(), 1);
+    let fk = &orders.foreign_keys[0];
+    assert!(fk.ref_table.contains("users"));
+    assert_eq!(fk.on_delete, "CASCADE");
+    assert_eq!(snap.views.len(), 1);
+    assert!(snap.views[0].definition.contains("SELECT"));
+}
+
+/// Live PG capture — mirror the env/client conventions of the live PG tests in
+/// `commands/objects.test.rs`. Create two diverged tables in a temp schema,
+/// assert capture shape (columns with defaults, PK, FK with actions, indexes,
+/// views, a sequence, an enum).
+#[tokio::test]
+#[ignore]
+async fn pg_capture_live() {
+    let h = std::env::var("GRIDLINE_TEST_PG_HOST").expect("set GRIDLINE_TEST_PG_HOST");
+    let p: u16 = std::env::var("GRIDLINE_TEST_PG_PORT").unwrap_or_else(|_| "5432".into()).parse().unwrap();
+    let u = std::env::var("GRIDLINE_TEST_PG_USER").expect("set GRIDLINE_TEST_PG_USER");
+    let d = std::env::var("GRIDLINE_TEST_PG_DB").expect("set GRIDLINE_TEST_PG_DB");
+    let pw = std::env::var("GRIDLINE_TEST_PG_PASSWORD").unwrap_or_default();
+    let (client, conn) = tokio_postgres::connect(
+        &format!("host={h} port={p} user={u} dbname={d} password={pw}"),
+        tokio_postgres::NoTls,
+    )
+    .await
+    .expect("connect to test PG");
+    let handle = tokio::spawn(async move { let _ = conn.await; });
+
+    let schema = "gridline_diff_test";
+    client
+        .batch_execute(&format!(
+            "DROP SCHEMA IF EXISTS {schema} CASCADE; CREATE SCHEMA {schema};"
+        ))
+        .await
+        .expect("create temp schema");
+
+    // Two diverged tables: one with PK/FK/index/default, one plain.
+    client
+        .batch_execute(&format!(
+            "CREATE TABLE {schema}.parent (id serial PRIMARY KEY, code text UNIQUE);
+             CREATE TABLE {schema}.child (
+                id serial PRIMARY KEY,
+                parent_id integer REFERENCES {schema}.parent(id) ON DELETE CASCADE ON UPDATE RESTRICT,
+                name text NOT NULL DEFAULT 'x',
+                email text
+             );
+             CREATE INDEX idx_child_email ON {schema}.child(email);
+             CREATE VIEW {schema}.v_child AS SELECT id, name FROM {schema}.child;
+             CREATE SEQUENCE {schema}.seq_test START 5 INCREMENT 2;
+             CREATE TYPE {schema}.mood AS ENUM ('happy', 'sad');"
+        ))
+        .await
+        .expect("create objects");
+
+    let snap = capture_pg(&client, "postgresql", schema).await.expect("capture");
+    assert_eq!(snap.engine, "postgresql");
+    assert_eq!(snap.schema, schema);
+    assert_eq!(snap.tables.len(), 2);
+
+    let child = snap.tables.iter().find(|t| t.name == "child").expect("child table");
+    assert_eq!(child.primary_key, vec!["id"]);
+    assert!(child.columns.iter().any(|c| c.name == "name" && !c.nullable && c.default_value.is_some()));
+    assert!(child.columns.iter().any(|c| c.name == "email" && c.nullable));
+    assert!(child.indexes.iter().any(|i| i.name == "idx_child_email"));
+    assert_eq!(child.foreign_keys.len(), 1);
+    let fk = &child.foreign_keys[0];
+    assert!(fk.ref_table.contains("parent"));
+    assert_eq!(fk.on_delete, "CASCADE");
+    assert_eq!(fk.on_update, "RESTRICT");
+
+    let parent = snap.tables.iter().find(|t| t.name == "parent").expect("parent table");
+    assert!(parent.uniques.iter().any(|u| u.kind == "unique"));
+
+    assert!(snap.views.iter().any(|v| v.name == "v_child"));
+    assert!(snap.sequences.iter().any(|s| s.name == "seq_test" && s.start == "5"));
+    assert!(snap.enums.iter().any(|e| e.name == "mood" && e.labels == vec!["happy", "sad"]));
+
+    client
+        .batch_execute(&format!("DROP SCHEMA {schema} CASCADE;"))
+        .await
+        .expect("drop temp schema");
+    let _ = handle;
+}

desktop/src-tauri/src/models/db_viewer.rs

@@ -345,6 +345,125 @@ pub struct Relationship {
     pub cardinality: String,
 }
 
+// ---------------------------------------------------------------------------
+// Schema diff (0.8.0)
+// ---------------------------------------------------------------------------
+
+#[derive(Debug, Clone, Serialize, Deserialize, Default, PartialEq)]
+pub struct SnapshotColumn {
+    pub name: String,
+    pub data_type: String,
+    pub nullable: bool,
+    pub default_value: Option<String>,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize, Default, PartialEq)]
+pub struct SnapshotIndex {
+    pub name: String,
+    pub columns: Vec<String>,
+    pub unique: bool,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize, Default, PartialEq)]
+pub struct SnapshotFk {
+    pub name: String,
+    pub columns: Vec<String>,
+    pub ref_schema: String,
+    pub ref_table: String,
+    pub ref_columns: Vec<String>,
+    pub on_delete: String,
+    pub on_update: String,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize, Default, PartialEq)]
+pub struct SnapshotConstraint {
+    pub name: String,
+    /// "unique" | "check"
+    pub kind: String,
+    /// check: expression; unique: comma-joined columns
+    pub definition: String,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize, Default, PartialEq)]
+pub struct SnapshotTable {
+    pub schema: String,
+    pub name: String,
+    pub columns: Vec<SnapshotColumn>,
+    pub primary_key: Vec<String>,
+    pub uniques: Vec<SnapshotConstraint>,
+    pub checks: Vec<SnapshotConstraint>,
+    pub indexes: Vec<SnapshotIndex>,
+    pub foreign_keys: Vec<SnapshotFk>,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize, Default, PartialEq)]
+pub struct SnapshotView {
+    pub schema: String,
+    pub name: String,
+    pub definition: String,
+    pub materialized: bool,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize, Default, PartialEq)]
+pub struct SnapshotSequence {
+    pub schema: String,
+    pub name: String,
+    pub start: String,
+    pub increment: String,
+    pub minimum: String,
+    pub maximum: String,
+    pub cycle: bool,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize, Default, PartialEq)]
+pub struct SnapshotEnum {
+    pub schema: String,
+    pub name: String,
+    pub labels: Vec<String>,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize, Default, PartialEq)]
+pub struct SchemaSnapshot {
+    /// "postgresql" | "mysql" | "mariadb" | "sqlite" — the CONNECTION's db_type
+    pub engine: String,
+    pub schema: String,
+    pub tables: Vec<SnapshotTable>,
+    pub views: Vec<SnapshotView>,
+    pub sequences: Vec<SnapshotSequence>,
+    pub enums: Vec<SnapshotEnum>,
+    pub object_count: usize,
+    pub truncated: bool,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize, PartialEq)]
+pub struct DiffDetailLine {
+    pub label: String,
+    pub old: String,
+    pub new: String,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize, PartialEq)]
+pub struct DiffItem {
+    /// "table" | "column" | "constraint" | "index" | "view" | "sequence" | "enum"
+    pub object_type: String,
+    /// For column/constraint/index items: "<table>.<name>"; else the object name
+    pub name: String,
+    /// "added" | "removed" | "changed"
+    pub kind: String,
+    pub detail: Vec<DiffDetailLine>,
+    /// Target-side statements (usually exactly one per item)
+    pub sync_sql: Vec<String>,
+    pub destructive: bool,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct DiffReport {
+    pub items: Vec<DiffItem>,
+    pub source_label: String,
+    pub target_label: String,
+    pub truncated: bool,
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;